1. Field of the Invention
The present invention generally relates to the field of integrated circuits (ICs), and particularly to built-in self test (BIST) circuits embedded in ICs for implementing self-test routines.
2. Description of the Related Art
The testing of ICs after manufacturing has a significant impact on the overall IC production costs. As the ICs become more and more complex, test routines for properly and extensively testing the ICs increase in number and complexity. The kind of tests to be conducted necessarily varies from IC to IC. Expensive test equipment is thus needed.
In order to at least partly relieve the test equipment of the burden of conducting all the test phases, on-chip test circuitry is provided in the ICs for autonomously conducting part, if not all, of the test. This circuitry is commonly referred to as built-in self test (BIST) circuitry.
Two approaches are normally followed in designing a BIST circuitry.
According to a first approach, for every kind of IC (e.g., stand-alone memories, which can be DRAMs, SRAMs, EPROMs, Flash memories, EEPROMs, microprocessors, microcontrollers with embedded RAM and ROM, etc.) a dedicated BIST circuitry is developed. The BIST circuitry, being specific and customized for that IC, is fast in conducting the required tests, but it is not flexible, and cannot be straightforwardly exploited in different ICs. The design efforts made for developing the dedicated BIST circuit are high, and the dedicated BIST circuit cannot be easily re-used in different ICs.
In a second approach, a general purpose microprocessor is embedded in the IC to be tested. This solution is highly flexible, since a general purpose microprocessor can in principle run every test routine on every IC. However, due to the very fact that the microprocessor is designed for a general purpose, it is not normally optimized for speeding up the test routines on specific ICs; in order to reduce the test time, a high-performance microprocessor is needed (e.g., high clock frequency, RISC, 32-bit or more data word, etc.): the IC area overhead caused by the provision of a high-performance microprocessor can soon become unacceptable.